1. Field of the Invention
The invention relates to generally tubular bags, or liners, made of flexible plastic film and used to line a rigid or semi-rigid receptacle such as a waste bin or other collection receptacle. More particularly, the invention relates to a bag having one or more pleats fixed at points around the mouth portion of the bag to reduce the circumference of the mouth of the bag relative to that of the body portion of the bag. When the bag is placed into a supporting receptacle, such as a waste or recycling bin for example, the reduced mouth portion of the pleated bag may be fitted onto the rim of the receptacle and the top portion of the bag will then more securely engage with the receptacle. The bag is thereby more securely held to the support and the mouth portion of the bag is more securely held in an open state. The invention further relates, in certain embodiments thereof to a reduced mouth pleated bag which is configured to have one or more stress and strain modifying tabs positioned around the mouth portion of the bag. Each tab is intended to reduce the possibility of tearing of the bag at and near the conjunction of a seam and mouth portion of the bag during installation and service of the bag.
2. Description of the Prior Art
A bag used as a liner is typically supported by a rigid or semi-rigid structure such as a waste bin or other collection receptacle. When in service, it is usually convenient that the mouth portion of the bag stay open in order to allow the articles to be passed conveniently and unhindered into or out of the bag. Owing to the flexible, pliant nature of a plastic film, a plastic bag is generally not self supporting, nor is the mouth portion of a bag able to reliably remain in an open state on its own. Therefore, it is common to both support the bag, and at the same time keep the mouth portion of the bag open, by folding the top portion of the bag over the rim of a corresponding mouth or opening in the supporting structure. Unfortunately, this method of supporting the bag and bag mouth is often attended with a tendency for the top portion of the bag to slide or fall off, or otherwise disengage from, the supporting structure. When the top portion of a bag slips from its support in such manner, the bag may then cease to accomplish one or more of the functions for which it was intended.
1. Neckdown Bags
The present invention relates to a category of bag or liner having retaining means which rely primarily on the circumference of the mouth portion of the bag being less than that of the body of the bag. Hereinafter, bags or liners utilizing this retaining means will be referred to as xe2x80x9cneckdownxe2x80x9d bags. For a bag used as a liner, it is usually convenient and economical that the bag have a body that is larger in circumference than that of a supporting structure or receptacle into which the bag is placed. However, in this case the top portion of the bag, when folded over a rim or lip of the supporting structure, may yield a loose fit at best, and therefore offer little additional support for the bag. A reduced circumference mouth portion of a neckdown bag greatly aids in supporting the bag on all manner of supporting structures, especially if the reduced circumference portion is approximately equal or less than that of the supporting structure. In this case the reduced mouth portion can more readily engage the support and thereby provide additional support for the bag whilst the larger circumference body portion of the bag can remain adequately sized to fit the receptacle.
Some neckdown bags or liners utilize one or more elastic members, or bands, permanently engaged with, or bonded to the bag, and sized so that the elastic member will elastically stretch around and grip a supporting structure. Such constructions are disclosed for example in Eby et al (U.S. Pat. No. 4,509,570), Cortese (U.S. Pat. No. 4,953,704), and Perkins (U.S. Pat. No. 4,747,701). Perkins in U.S. Pat. No. 4,747,701 asserts that in some xe2x80x9cliner bagsxe2x80x9d, the slight elasticity of the plastic itself will aid in holding the bag in place, that some bags will stretch to a small extent so that they are held tightly when folded over the rim of a receptacle. It is further asserted that the elasticity of the typical liner bag is relatively low and the bags will often tear when pulled too hard. These perceived drawbacks of a typical liner bag film force the design of the bag disclosed to require an xe2x80x9celastic bandxe2x80x9d or head member to be permanently attached to the bag body. Typical materials disclosed for the elastic band are xe2x80x9celastomersxe2x80x9d such as xe2x80x9clatexxe2x80x9d (a rubber elastomer) and xe2x80x9cDUREFLEX(trademark) PT6100Sxe2x80x9d (of Deerfield Urethane, Inc.) an aromatic polyether polyurethane film which is a thermoplastic elastomer. An elastomer film exhibits a rubber-like elastic deformation response, that is, it can greatly elongate upon the application of a relatively weak stretching force, and upon removal of this stretching force, the film quickly recovers substantially its original shape and size, mimicking the familiar action of a rubber band being stretched and then released. The elastic band is required to be bonded to a relatively inelastic bag body in order to achieve a functional self gripping neckdown liner. As the attached elastic band is required to perform the self retaining action, the elastic band, not the bag body, is made to have the neck down feature. It is apparent that such a bag design, while functional, is complicated by having the liner made of two distinct members, the relatively stiff bag body, and the elastic band or head member. The two members are required to be intimately attached along a common edge, leading to a necessary complexity in the bag structure and in the manufacture of such a liner bag.
It is known that a bag having a reduced size mouth relative to the body of the bag can be constructed by joining together portions along the top of the bag to form a pleated neckdown bag having reduced circumference mouth portion relative that of the bag body. Imazeki et al (U.S. Pat. No. 4,919,546) discloses such a method to obtain a neckdown bag, as does Perkins in U.S. Pat. No. 4,747,701 already cited above. Disadvantages are apparent in Inazeki et al in that the bag supporting function relies strictly on the principle that the bag body material is xe2x80x9cnon-elasticxe2x80x9d, or inelastic, and thereby can bear no stretching either on installation of the bag to its support, or while the bag is being supported. The xe2x80x9cnon-elasticxe2x80x9d limitation requires the use of a specially engineered hoop-like support to be designed and then installed in a specified way so as to avoid any stretching of the bag, thereby affording a purely kinematic constraint to secure the liner to the support. The need for the hoop support greatly limits the types of support receptacles that can be used with the bag and increases the complexity and cost of such a system.
Kaczerwaski (U.S. Pat. No. 4,611,350) discloses a closed bottom xe2x80x9csackxe2x80x9d of thermoplastic film comprising at least one cold stretched, circumferential band portion of diameter that is reduced from the original diameter of the sack. The band of reduced diameter is obtained by cold stretching the film so as to procure, through a permanent material xe2x80x9cnecking-downxe2x80x9d phenomenon, a circumferential band of reduced diameter in the region adjacent to the bag mouth opening (the xe2x80x9cnecking-downxe2x80x9d term used to describe the phenomenon disclosed in Kaczerwaski is a term of art in the science of materials and is not to be confused with the similar xe2x80x9cneckdownxe2x80x9d term used herein to refer to a particular construction of a bag). The reduced band region of the bag can be positioned relative to the bag mouth so as to accommodate a more secure, gripping overfold region when the bag is employed as a waste container liner. The method disclosed is limited to materials that will neck-down when cold stretched. Another drawback to this method is that there is a limit to the degree of reduction of bag diameter that can be achieved with the method disclosed and the method requires highly specialized equipment to introduce the necking-down phenomena to the bag.
It is generally known that a self securing neckdown bag is obtainable by the common practice of xe2x80x9ctying offxe2x80x9d corners of a bag mouth using one or more overhand knots. This action creates a reduced or neckdown mouth opening thus allowing the bag mouth to be securely fitted over a supporting structure or receptacle. The knot method of forming a neckdown bag does not lend itself to mass production or convenient bulk packaging, and can become cumbersome for large liners or liners having heavy walls. Moreover, this method can be difficult or impossible to implement for someone unable to effect the knot due to lack of dexterity possibly due to physical impairment such as arthritis or a Repetitive Stress Injury. Further, one involved in the cleaning or janitorial service industry using this method will be forced to tie knots many times a day possibly leading eventually to a Repetitive Stress Injury as a result of the excessive repetition of tying many knots over long periods. The tying off method results in one or more unsightly xe2x80x9cpigtailsxe2x80x9d, left on the outer rim of the support by the existence of the knot or knots. Finally, the use of a knot in a neckdown bag may require an excess of film material to be used in order to make up the knot, and thereby result in a liner having an effectively shorter length which may then not fit the support or bin, or may require a longer liner and therefore a wastage of bag film material.
2. Tearing of Plastic Film Bags
When a pleated neckdown bag is initially fitted onto a supporting receptacle, the bag film at and near the mouth portion of the bag is susceptible to tearing, especially at any seam restricting the mouth portion. Because the plastic film at and near the mouth portion of the neckdown bag continues supporting the bag and bag mouth during the service life of the bag, the film is apt to tear when the bag is in service as well. The propensity for tearing of the bag film is thought to be most acute about the mouth portion, particularly at a seam intersecting the mouth. This is because the forces applied to the bag mouth on installation, and the possibility of somewhat lessened film strength in or near a seam, results in a relatively increased possibility of tearing the plastic film at or near this location more so than at other points around the mouth. A tear, once initiated, may then continue to propagate preferentially along the seam and may then impair the neckdown feature and, hence, reduce or eliminate the advantages obtained thereby.
Methods to minimize or eliminate tearing of a bag at or near a seam, or for rendering this tearing harmless, are disclosed. For example R. A. Gruentzel et al (U.S. Pat. No. 3,485,437) discloses a method to render harmless the tearing of a weakened seam, at its terminus at the mouth of a bag, by providing for a second weakened area, either a slit, scored, or thinned region, being located near the first weakened area, but spaced from it. When tensional forces cause the seam at the mouth to tear, the tear is arrested, by the second weakened area, from further propagation along the seam, and the tear is redirected away from the seam into presumably stronger regions of the bag, where the tear is presumably arrested or minimized. The method of providing a second weakened area, as in U.S. Pat. No. 3,485,437, while it can control a tear by redirecting it away from the seam, does not necessarily eliminate the occurrence of a tear. Such a tear, even if it is redirected away from the seam, could still be detrimental to the retaining function of a neckdown bag.
Rasmussen (U.S. Pat. No. 5,202,650) discloses placing a band of embossed indentations adjacent a seam xe2x80x9csusceptible to rupture when stressedxe2x80x9d so that the band, being xe2x80x9cmore rubberlikexe2x80x9d than the unmodified material, may increase the resistance of the seam to rupture under stress. The method of providing a band of indentations certainly might be useful for preventing tearing of a seam in a neckdown bag, however such a method requires additional specialized film embossing machinery perhaps not normally required in the manufacture of plastic film bags or liners.
In accordance with the present invention a pleated neckdown bag made of a flexible plastic film, and for lining a receptacle, is disclosed wherein the neckdown feature of the bag is constructed by pleating the bag inwardly at one or more points around the mouth portion. Two side, or flank, portions of a given pleat portion of the bag are joined together along the top portion of the bag. The joining means interconnecting the flanks of a pleat will generally form a seam, or seam portion, partway across the top portion of the bag, the seam perhaps comprising a heat or fused seal, adhesive bond, or a joinder. The inwardmost portion or end of such a seam portion, that is the end nearest or adjacent the mouth of the bag, effectively restricts the mouth portion so that the circumference of the mouth portion is substantially less than that of the body portion of the bag. The neckdown bag can be expanded and the reduced circumference mouth portion fitted over a supporting receptacle. The top portion of the bag is thereby more securely held to the support, and the mouth portion is more securely held in an open state, since the narrowed mouth portion of the bag can better engage a support such as the rim of a waste or other collection receptacle. Bag embodiments are disclosed having flat constructions and flat rectangular constructions, both convenient for manufacture, packaging, storage, and dispensing.
Certain disclosed embodiments of the present invention provide for a xe2x80x9ctabxe2x80x9d, that is, a xe2x80x9cfinlikexe2x80x9d extension of a portion of a bag adjacent an edge defining a mouth edge of the bag. Each tab is arranged about the mouth portion of the bag so that the tab projects from a tab base, defined between first and second reentrant arcuate portions of a mouth edge, and a top seam portion of the bag extends across the tab base and into the tab. Such a tab will advantageously modify the stress and strain in the bag at and near the tab so as to reduce the possibility of tearing the seam or mouth portion of the bag in the neighborhood of the tab. A particular tab embodiment is also disclosed that offers tear protection while allowing the bag to retain a typical xe2x80x9cflatxe2x80x9d construction.
Objects and Advantages
It is the object of the present invention to provide a pleated neckdown bag for lining a receptacle, wherein the bag is made of a flexible plastic film. The narrowed, or neckdown, mouth portion of such a bag may be fitted onto the rim of a rigid or semi-rigid supporting receptacle, such as a waste bin, so the top portion of the bag more reliably engages with the supporting receptacle, and the mouth portion of the bag is more securely held in a generally open state. In certain embodiments, the invention has the further object to construct and employ a pleated neckdown bag made of a typical low cost plastic bag film, such as a polyethylene based film. It is the further object, in certain embodiments of the invention, to provide a generally flat pleated bag construction that is relatively straightforward both to manufacture, and to package, especially by automated or semi-automated means, and lends itself to more convenient storage and dispensing. It is the further object of the invention, in certain embodiments thereof, to provide a pleated neckdown bag construction having one or more tabs for advantageously modifying stress and strain at and near the conjunction of a seam and mouth portion of a bag. Each tab is intended to reduce or eliminate the chance of tearing of the bag when in use, at or near the mouth and seam portions, where such tearing might be detrimental to the retaining function of the bag. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.